Invasive group A strep (iGAS)

Group A streptococcus is a common bacterium that causes throat infections, scarlet fever, impetigo and cellulitis. The NHS notes that strep A infections range from mild to serious and that most are mild and easily treated. In a small number of people the bacteria invade deeper tissue. Invasive disease can present as bloodstream infection, pneumonia with empyema, toxic shock syndrome, necrotising fasciitis or infection of bones and joints.

Invasive infections are uncommon, but numbers have fluctuated over recent years, sometimes rising after periods when fewer children were circulating respiratory viruses and then returning to normal patterns.

The NHS lists people with weakened immunity, open wounds and concurrent viral illnesses such as colds as being at higher risk of a serious strep A infection. Chickenpox in young children is a well-recognised trigger for skin and soft-tissue invasive disease. Others at higher risk include people who inject drugs, those with diabetes, older people, people who have recently given birth and anyone with a recent surgical or skin wound.

Typical strep throat causes a high temperature, sore throat and swollen neck glands, and scarlet fever adds a sandpaper-like rash and strawberry tongue, according to the NHS. Warning signs that an infection may be becoming invasive include a child who is getting worse after a few days, severe pain out of proportion to a wound, a rapidly spreading red or purple skin area, drinking much less, signs of dehydration, a very high or very low temperature, fast breathing, confusion or floppiness.

The NHS says to seek urgent help if your child is getting worse, is feeding or drinking less than normal or shows signs of dehydration, and to call 999 for breathing difficulty, unconsciousness or blue skin, tongue or lips.

• Worsening illness after initial improvement.

• Severe pain or swelling around a wound, with rapidly spreading redness.

• Fast or difficult breathing.

• Drowsiness, confusion, floppiness or a cold mottled appearance.

• Reduced urine output or very reduced drinking.

Invasive group A strep is a medical emergency. Treatment usually includes intravenous antibiotics started quickly, fluids to support circulation, oxygen, and sometimes additional antibiotics that reduce toxin production. Surgery is needed for necrotising fasciitis or collections of pus. Some patients need intensive care. The NHS notes that more serious infections may be treated with antibiotics, and people with scarlet fever who are prescribed them recover faster and are less likely to develop serious illness such as pneumonia.

Close contacts may be offered antibiotics in some circumstances, such as household contacts of a case of invasive disease or in settings such as maternity units, on the advice of the local health protection team.

The NHS lists complications of untreated group A strep including ear infection, throat abscess, sinusitis, pneumonia, meningitis and rheumatic fever. Rheumatic fever and kidney inflammation after strep infection are immune reactions that can appear weeks later, which is why the NHS advises seeing a GP if illness returns weeks after scarlet fever. Recovery from invasive disease can be long and may need rehabilitation.

Strep A spreads through coughs and sneezes and contact with infected skin or wounds. The NHS advises frequent handwashing, using tissues and avoiding close contact with infected people. After starting antibiotics, stay away from school, nursery or work for 24 hours. A person with scarlet fever is contagious for 24 hours after starting antibiotics, or for 2 to 3 weeks without treatment. Keep wounds clean and covered, and ask a pharmacist or GP about chickenpox in young children who then develop a red, painful area of skin.